Both these cartridges seem very similar, ballistically. The 338 seems to be a little faster and the only difference between it and the .358 is bore size. Which one is a better round to load for and use for all around big game use? I'm in the north east so I don't have the opportunity to take extremely long range shots. The farthest I've calculated external ballistics out to is 350yd.
At 77 years of age, after over 60 years of owning hunting rifles, reloading, a having some fine custom rifles made, only one custom hunting rifle project interests me.
Before going further, let me say that my all-time favorite rifle in hand outdoor adventures came with two custom 35 Whelen's. On three different trips I took one to Alaska for a live off the land adventure. Each trip I paid $20 for my nonresident small game license.
Further for decades I did most all my hunting with one of these 35 Whelen's. I loved hunting antelope in mountain meadows of NW Wyoming. It was Grizz country and I felt comforted having my Whelen.
So back to my final custom rifle project.
I would get a Sako 75 Finnlight in a 308. or 7mm-08 and have a custom barrel made for it in 358 Winchester, with a 1/16 twist. I had a Remington Classic in 35 Whelen with this twist. It shot the Barnes 225 grain TSX well under MOA. It also shot the 158 grain lead round nose bullets very well for small game with a light load of Unique. My other Whelen was the 1/14 twist and the lead small game bullets were nowhere near as accurate.
Also, the 1/6 twist permitted shot loads mixed with 6's an 8's shot size to be reasonable for quail and grouse up close.
This twist handled 38 and 357 bullets as well.
The Sako Action, allowed bullets to be dropped in and push fed, and If one looks with patience, you will find those Sako peep sights. Of course, a front sight will be needed. Lastly, again with patience look for some original Sako Opitlock rings in extra low.
There is nothing anywhere that such a rig cannot do. Mine shot just fine out to 350 yards, and the big game I shot with it never needed more than one shot.